Evans MS et al. – These results build on previous work indicating that TRPV1 channels in trigeminal nociceptors play a role in craniofacial pain. These findings that TRPV1 is inhibited by the specific antimigraine drug sumatriptan, and that TRPV1 channels are functional in neurons projecting to cerebral dura suggests a specific role for these channels in migraine or cluster headache.

Methods

Authors used immunohistochemistry to detect the presence of TRPV1 channel protein, whole–cell recording in acutely dissociated trigeminal ganglia (TG) to detect functionality of TRPV1 channels, and whole–cell recording in trigeminal nucleus caudalis (TNC) to detect effects on release of neurotransmitters from trigeminal neurons onto second order sensory neurons.

Effects specifically on TG neurons that project to cerebral dura were assessed by labeling dural nociceptors with DiI.

Results

Immunohistochemistry demonstrated that TRPV1 channels are present in cerebral dura, in trigeminal ganglion, and in the TNC.

Capsaicin, a TRPV1 agonist, produced depolarization and repetitive action potential firing in current clamp recordings, and large inward currents in voltage clamp recordings from acutely dissociated TG neurons, demonstrating that TRPV1 channels are functional in trigeminal neurons.

Capsaicin increased spontaneous excitatory postsynaptic currents in neurons of layer II in TNC slices, showing that these channels have a physiological effect on central synaptic transmission.